Morphological methods were used for the study of epithelial-stromal relations, free cells, lymphocyte population and endocrine cells of the colon during the stage of remission andexacerbation in patients with nonspecific ulcerative colitis (NUC). An increase of the total population of endocrine cells (with domination of serotonin-containing cells) in all altered parts of the colon was in chronic NUC. Disturbance of cooperation between the free stromal cells and epithelial components, correlation between population of T and B lymphocytes, increased number of CD8+ cells were seen in NUC exacerbation this being the basis of chronization and progression of this disease.